Chucking device and brushless motor and disc driving device in which the chucking device is installed

ABSTRACT

A cone part in a chucking device capable of freely attaching and detaching a disc having a disc shape includes an abutting portion for abutting an inner peripheral surface of a central through hole of the disc with substantially equal forces along an entire circumference thereof and aligning the disc. The cone part is made of a resin material having a high slidability than that of a material used for the disc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.11/491,965 filed Jul. 25, 2006, which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2005-215437 filed Jul. 26, 2005 and Japanese Patent Application No.2006-185842 filed Jul. 5, 2006, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chucking device for making a dischaving a disc shape freely attachable and detachable and a brushlessmotor and a disc driving device in which the chucking device isinstalled.

2. Description of the Related Art

In recent years, development of DVD having large capacity as anext-generation DVD (Digital Versatile Disc) for recording ahigh-quality image demanding a large capacity has been aggressivelypromoted. In the high-capacity DVD, the high capacity is realized insuch a manner that a track pitch is changed from 0.64 μm which wasconventionally adopted to 0.32 μm which is a half of the conventionallength, and a blue-violet laser having a short wavelength iscorrespondingly used as a laser for recording and reproduction in placeof a red laser having a long wavelength which was conventionally used sothat a recording density is increased. Further, the high-capacity DVD isrotated at such a high speed as 10,000 rotations per minute so that arecording speed is increased and a high double speed is realized in theDVD.

In order to retain the recording disc such as the high-capacity DVD, abrushless motor provided with a chucking device for retaining an innerperipheral edge of a central through hole of the recording disc using aplurality of retaining parts having a claw shape or the like andenergized by a spring was conventionally adopted.

However, in the chucking device for retaining the recording disc usingthe plurality of claws, in which only the retaining parts having theclaw shape or the like and radially protruded are used to retain theinner peripheral edge of the central through hole of the recoding disc,each retaining part has a different retaining force for retaining theinner peripheral edge of the central through hole of the recording disc.As a result, an aligning accuracy of the recording disc is deterioratedwhen the recording disc is rotated at such a high speed as 10,000rotations per minute or in the case where a balancing performance of therecording disc is remarkably inferior. Due to the disadvantage, thehigh-capacity DVD as the next-generation DVD possibly included thedisadvantage that an error occurred in recording and reproduction.

In addition to the foregoing disadvantage, in the chucking device, inthe case where the recording disc loses even a slight balance whenrotated at such a high speed as 10,000 rotations per minute, theretaining parts and the inner peripheral edge of the central throughhole of the recording disc strongly abut each other in one direction bya centrifugal force. This makes positions at which the retaining partsand the recording disc abut each other shifted, which also shifts aposition of the recording disc. As a result, a recording/reproducingposition changes in an initial stage of the rotation and during therotation, which possibly caused an error in the recoding andreproduction. The worst possible incident was that the recording discwas possibly disengaged from the chucking device. Further, such aphenomenon that the recording disc and the retaining parts unfavorablybite into each other and move together is generated under the influenceof the centrifugal force. When the biting phenomenon is generated, aforce which returns a cone part to its original position is enhanced bya reaction generated from the phenomenon, and the recording disc israpidly returned to its original retaining position at a moment when theforce becomes stronger than the force in the meshing direction. As aresult, the drastic position shift of the recording disc makes itimpossible for a reading function of the recording disc to follow theposition shift of the recording disc, which may cause an error in therecording and reproduction. Further, if the retaining force of therecording disc is weak, a vibration is generated between the recodingdisc and the chucking device when the recording disc is rotated at ahigh speed. The vibration makes the recording disc rotate while movingthe disc by a minute distance, which also possibly caused an error inthe recording and reproduction.

BRIEF SUMMARY OF THE INVENTION

A chucking device according to the present invention is characterized inthat a material having a high slidability with respect to a discconstitutes a cone part in contact with the disc.

The cone part is a member which is made to abut an inner peripheralsurface of a central through hole of the disc so that the disc isaligned to a central position and retained there.

In a conventional chucking device of the same type, a metal member, forexample, was used as the material constituting the cone part in order tofirmly retain the disc.

In the present invention, the slidability is aggressively impartedbetween the cone part and the disc. Accordingly, displacement of thedisc with respect to the cone part can be prevented particularly whenthe disc is rotated at a high speed, and the disc can be more smoothlyled to the central position of the chucking device when the disc isattached.

A surface roughness Ry of the cone part desirably satisfiesapproximately 5 μm Ry approximately 20 μm. Further, it is desirable thatthe disc be made of polycarbonate, and a coefficient of static frictionμ at a part where the cone part and the disc abut each other satisfyapproximately 0.15≦μ≦approximately 0.30.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view in an axial direction of abrushless motor according to a preferred embodiment of the presentinvention.

FIG. 2 is an enlarged view of a chucking device shown in FIG. 1.

FIG. 3 is a graph showing a result of a test for measuring a frictionalforce when a surface roughness is increased.

FIG. 4 is a graph showing a result of measurement of a spring forcenecessary for preventing occurrence of an error in the disc atrespective numbers of rotations.

FIG. 5 shows a test result in which the disc was repeatedly attached anddetached depending on materials used for the cone part.

FIG. 6 Shows a schematic sectional view in the axial direction, whichshows a state where the laminated disc D is placed in FIG. 2.

FIG. 7 shows a state where a laminated disc is attached to the chuckingdevice shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Overall Structure of BrushlessMotor

A brushless motor according to the present invention is describedreferring to FIG. 1. FIG. 1 is a schematic sectional view illustrating apreferred embodiment of the brushless motor according to the presentinvention.

First, a fixed member is described.

An annular step part 11 is provided on a lower surface of a sleeveretaining member 10 having a cylindrical shape provided with a bottomand an opening in an upper direction and formed by means ofoil-impregnated sintering. An annular washer 20 is provided on an uppersurface of the annular step part 11 so as to abut the surface, while adisc washer 21 is provided at the bottom part 12 of the annular steppart 11 so as to abut the part.

A cylindrical sleeve 30 is fixedly provided so as to abut an innerperipheral surface of a cylindrical part 13 of the sleeve retainingsection 10 and an upper surface of the annular washer 20. The sleeve 30is made of an oil-impregnated sintered material. An upper end part ofthe cylindrical part 13 is provided with an extended part 14 extendingradially outward, and an inner periphery annular step part 15 is formedon an inner-peripheral side of the extended part 14. A washer 40 isprovided in the inner periphery annular step part 15 so as to cover anupper surface of the sleeve 30. The washer 40 is provided in order tolead oil oozed from the sleeve 30 back to the sleeve 30 again.

An armature 50 formed in an annular shape is secured to an outerperipheral surface of the cylindrical part 13 of the sleeve retainingsection 10. On a lower side of the armature 50, a mounting plate 60 forsecuring the brushless motor to the other components is secured to theouter peripheral surface of the cylindrical part 13. A circuit substrate70 for controlling rotation of the brushless motor is secured to anupper surface of the mounting plate 60.

Next, a rotational member is described.

A shaft 80 is insertably provided on an inner peripheral surface of thesleeve 30, and the sleeve 30 rotatably supports the shaft 80. To anupper part of the shaft 80 are secured a cylindrical rotor holder 90having a cap and an opening in a lower direction so as to externallysurround the sleeve retaining section 10, sleeve 30 and armature 50. Apreload magnet 100 having an annular shape is secured to a surface of acap part 91 of the rotor holder 90 axially facing the extended part 14of the sleeve retaining section 10. Further, a rotor magnet 110 havingan annular shape is secured to an inner peripheral surface of acylindrical part 92 of the rotor holder 90. An inner peripheral surfaceof the rotor magnet 110 and an outer peripheral surface of the armature50 face each other with a radial interval therebetween.

A chucking device 120 for aligning and retaining a disc having a discshape (not shown) is secured to an upper surface of the cap part 91 ofthe rotor holder 90.

When a current is supplied to the armature 50 from outside, the armature50 generates a magnetic field, and the rotational member, which obtainsa driving force through an interaction between the magnetic field andthe rotor magnet 110, is rotated.

Structure of Chucking Device

A structure of the chucking device 120, which is a main component of thepresent invention, is described referring to FIG. 2. FIG. 2 is anenlarged view of the chucking device 120 shown in FIG. 1. A dotted anddashed line shown in FIG. 2 denotes a central axis which is a rotationalaxis. FIG. 3 is a graph showing a frictional coefficient with respect toa surface roughness measured according to a frictional coefficientmeasuring method defined by the Japanese Industrial Standards. FIG. 4 isa graph showing a spring force necessary for number of rotations perunbalancing load of the disc.

Referring to FIG. 2, the chucking device 120 includes a turn table 121on which the disc is placed, a cone part 122 for retaining the disc, aspring 123 for axially energizing the cone part 122, and a yoke section124 which is a movement regulator for regulating an axial movement ofthe cone part 122.

The disc is placed on the turn table 121 while an inner peripheral edgeof a central through hole thereof is retained by the cone part 122. Anupper surface of the disc is controlled by a clamp (not shown) so thatthe disc is further retained.

1) Turn table

The turn table 121 secured to the upper surface of the cap part 91 ofthe rotor holder 90 has a central through hole and is position-securedto be concentric to the rotational axis when pressed into the shaft 80.Three recessed portions respectively deepened from the outer side towardthe center and having different diameters are formed at a central partof the turn table 121, and they are respectively referred to, from theinner side, as a first recessed portion 121 a, a second recessed portion121 b and a third recessed portion 121 c. These recessed portions serveto house the cone part 122 without applying any restriction to themovement of the cone part 122 when the cone part 122 moves downward.Further, an annular disc rubber 125 made of an elastic material such asrubber, which serves as a surface on which the disc is placed, issecured an outer-peripheral side upper surface of the turn table 121.

2) Cone Part

The cone part 122 provided on an upper side in comparison to the threerecessed portions of the turn table 121 comprises a sliding part 122 ahaving a central through hole and a sliding surface on an innerperiphery thereof, a coupling part 122 b extending radially outward andaxially upward, and a retaining part 122 c for retaining the disc.

Through hole of the sliding part 122 a is inserted into an outerperipheral surface of the shaft 80 to be concentric to the central axis.The sliding surface, which is the inner peripheral surface of thethrough hole and slides with the shaft 80, faces the outer peripheralsurface of the shaft 80 with a very small radial interval therebetween.In the case where a sliding agent is filled into the very smallinterval, the cone part 122 can more smoothly axially move. Thereby, thedisc can be smoothly attached and detached.

An upper surface of the retaining part 122 c is a tilting surfacetilting downward toward the outer side includes a guiding part 122 c 1for guiding the disc in an aligning manner and an abutting portion 122 c2 for abutting and retaining the disc, which is a tilting surfaceprovided more radially outward than the guiding part 122 c 1 and tiltingthrough an angle changed further downward.

The cone part 122 is made of a resin material. A coefficient of staticfrictional between an outer peripheral surface of the abutting portion122 c 2 of the retaining part 122 c and the inner peripheral surface ofthe central through hole of the disc is smaller than a coefficient ofstatic frictional between the outer peripheral surface of the abuttingportion 122 c 2 and the central through hole of the disc in the casewhere the cone part 122 is made of a metal material.

An angle φ formed by the tilting surface of the abutting portion 122 c 2and the central axis as the rotational axis is desirably at least 12degrees and at most 15 degrees (preferably 13.5 degrees). In the casewhere the angle range is set, an influence generated by a centrifugalforce acting on the abutting portion 122 c 2 when the disc is rotated ata high speed can be reduced. In particular, a component of force actingon the abutting portion 122 c 2 axially downward due to the centrifugalforce can be reduced. The downward movement of the cone part 122 can bethereby controlled, which consequently controls the displacement of thedisc. The angle φ is preferably as close to 0 degree as possible so thatthe force participating in the centrifugal-force direction can becontrolled by the tilt. However, the angle desirably stays in theforegoing range in order to retain the discs of any type because adiameter of the central through hole of the disc is variable to acertain extent depending on the type of the disc. When the angle is atmost the foregoing degree, the disc and the cone part may unfavorablybite into each other, resulting in the position-shift of the disc.Further, the disc having the central through hole whose diameter islarge cannot obtain a necessary retaining force. When the angle is atleast the degree, the positions of the disc and the cone part 122 shiftrelative to each other under the influence of the centrifugal forcebecause the disc loses its balance. More specifically, the force acts onthe abutting portion 122 c 2 due to the influence of the centrifugalforce, which moves the cone part 122 downward, and the disc, therebymoves to the upper side of the cone part 122, may be disengaged from thechucking device 120.

A surface roughness Ry of the tilting surface of the abutting portion122 c 2 is in the rage of Ry=5 μm-20 μm (preferably, Ry=10 μm-15 μm).The surface roughness Ry is a value obtained in such a manner that areference length is retrieved from a roughness curve in a direction ofan average line, and a distance between a top line and a bottom line ofthe retrieved part is measured in a direction of a longitudinalmagnification of the roughness curve.

Referring to FIG. 3, a relationship between the surface roughness andthe frictional force is described. FIG. 3 is a graph showing a resultobtained in such a manner that the disc is placed on resin, a bellhaving a predetermined weight (which is shown by load in the drawing) isplaced thereon, and a load at a moment when the bell is horizontallypulled and starts to move is measured as the frictional force.

It is known from the graph of FIG. 3 that the frictional force isreduced as the surface roughness is increased. Referring to the load ofeach bell, the frictional force is high when the surface roughness is atmost 5 μm, while the frictional force is drastically reduced as thesurface roughness is increased in the graph. However, the frictionalforce is gradually reduced as the surface roughness is increased whenthe surface roughness is at least 5 μm. Therefore, when the surfaceroughness is set to at least 5 μm, a low frictional force can be stablyobtained. As a result, the frictional coefficient between the abuttingportion 122 c 2 and the recording disc can be reduced, and a vibrationbetween the disc and the cone part 122 can be controlled. The axial andradial displacements of the disc, which result from the action of thedownward force on the disc and the abutting portion 122 c 2 generated inconsequence of the disc and the abutting portion 122 c 2 of the conepart 122 biting into each other due to the vibration, can be prevented.Then, the disc can be prevented from rapidly returning to its originalposition due to the displacements. Therefore, occurrence of an error inthe recording and reproduction when the disc is rotated at a high speedcan be prevented.

When the surface roughness is larger than 20 μm, the inner peripheraledge of the central through hole of the disc and the abutting portion122 c 2 of the cone part 122 scrape each other when the disc is attachedand detached, which wears the contact surfaces thereof when the disc isattached and detached. As a result, the position of the disc may axiallyshift when a large number of discs are repeatedly attached and detached.

Therefore, the surface roughness Ry of the tilting surface of theabutting portion 122 c 2 is desirably in the range of Ry=5 μm-20 μm(preferably, Ry=10 μm-15 μm) so that the abutting portion can stablyabut the disc with a small frictional force and the wear of the abuttingportion 122 c 2 and the central through hole of the disc can beprevented. Furthermore an axial surface roughness Rya of the abuttingportion in the cone part satisfies the relationship of approximately 5μm≦Ry≦20 μm. Here, the Rya is measured along the axial direction of thetilting surface of the abutting portion 122 c 2.

The surface roughness of the tilting surface of the abutting portion 122c 2 is desirably formed when a molding die is formed. In particular, asurface roughness of the molding die at a position where the abuttingportion 122 c 2 is formed is roughened so that the surface roughness ofthe tilting surface of the abutting portion 122 c 2 can be formed at thesame time as the formation of the molding die. Thereby, a step ofadjusting the surface roughness in the range of Ry=5 μm-20 μm, which isto be implemented after the molding die is formed, can be omitted, whichcontrols a processing cost of the cone part 122.

3) Spring

A spring 123 provided on an upper surface of the second recessed portion121 b of the tune table section 121 and abutting a lower side of theretaining part 122 c of the cone part 122 to thereby support the conepart 122. The spring 123 is made of a material having a superiorelasticity such as a coil spring or an elastic resin spring. In thepresent preferred embodiment, the coil spring is adopted.

FIG. 4 is a graph showing a spring force which makes the disc disengagedfrom the chucking device 120 during the rotation at respective numbersof rotations.

Referring to FIG. 4, the spring force of the spring 123 is desirably inthe range of at least 1.2 N and at most 2.0 N (preferably, 1.5N).Because the device was conventionally used for a low-speed rotation, theinfluence of the centrifugal force of the disc was small, and the springforce was correspondingly small. However, in the disc demanding such ahigh-speed rotation as 10,000 rotations per minute such as thehigh-capacity DVD, the disc strongly abuts the abutting portion 122 c 2of the cone part 122, and the component of force resulting from thecentrifugal force caused by the unbalanced disc is exerted axiallydownward. The conventional spring force was at most 1.2 N, which wassmall, a reaction against the component of force exerted axiallydownward, which results from the centrifugal force, was weak, which madeit easy for the cone part 122 to move downward, and the disc quitepossibly jumped out of the cone part 122. The disc can be thus easilyremoved from the cone part 122 when the spring force is smaller than 1.2N. Therefore, it is necessary to set the spring force to a large valuein order to counteract the component of force exerted axially downwardresulting from the centrifugal force. However, when the spring force islarger than 2.0 N, on the contrary, the abutting force between theabutting portion 122 c 2 of the cone part 122 and the disc is too large,which makes it difficult to attach the disc to the chucking device 120.Therefore, the spring force is set to at least 1.2 N and at most 2.0 Nreferring to the graph (preferably, 1.5 N) so that the downward movementof the abutting portion 122 c 2 due to the centrifugal force of the disccan be prevented. As a result, the motor capable of preventing thedisplacement and disengagement of the disc and having a high reliabilitycan be provided.

4) Yoke Section

The yoke section 124 formed by the magnetic member placed on the upperpart of the cone part 122 is pressed into the shaft 80 and securedthereto to thereby restrict the axially upward movement of the cone part122. A magnetic attraction force between the magnet installed on theclamp side and the yoke section serves as one of factors for retainingthe disc as a clamp force.

5) Coefficient of Static Friction

The coefficient of static friction between the inner peripheral edge ofthe central through hole of the disc and the abutting portion 122 c 2 ofthe cone part 122, which are made of polycarbonate, is set to at least0.15 and at most 0.30 (preferably, around 0.20). When the coefficient ofstatic friction is set to at least 0.15, the frictional force of acertain level can be secured between the disc and the cone part 122.Then, the disc can be prevented from sliding relatively axially upwardeven though the disc strongly abuts the cone part 122 in one directiondue to the influence of the centrifugal force thereof and the cone part122 thereby moves axially downward. As a result, the disc can beprevented from popping out of the chucking device 120. Further, when thecoefficient of static friction is set to at most 0.30, the disc and thecone part 122 can be prevented from biting into each other, which iscaused by the centrifugal force of the disc. As a result, the suddenposition shift of the disc can be controlled so that occurrence of anerror in the recording and reproduction when the disc is rotated at ahigh speed can be prevented.

6) Material for Cone part

Referring to FIG. 5, a material for the cone part 122 is described. FIG.5 shows a result of the disc displacement before and after a test inwhich the disc was attached and detached 30,000 times at normaltemperature. FIG. 5 further shows comparison of the cone part 122 madeof polycarbonate (hereinafter, referred to as PC), polycarbonateincluding glass (hereinafter, referred to as PC (including glass) andpolyacetal resin (hereinafter, referred to as POM).

Referring to FIG. 5, the disc displacements in the case of all of thematerials used before the test were: 0 mm for PC; 0.025 mm for POM; and0.025 mm for PC (including glass), which showed a very little differencein the respective materials. However, after the test, the discdisplacements in the case of PC and PC (including glass) wererespectively 0.125 μm and 0.075 μm, which showed large increases. Incomparison to these materials, the disc displacement was 0.025 beforeand after the test in the case of POM, and it is known from the resultthat there was no difference before and after the test. The frictionalcoefficient was low in the case of POM in comparison to PC and PC(including glass), which reduces the abutting force with respect to thedisc. As a result, the disc and the cone part 122 can be prevented frombiting into each other. Therefore, the disc displacement before andafter the test, which is shown in the result of FIG. 5, can becontrolled. Based on the foregoing outcome, POM is preferably used asthe material for the cone part 122.

7) Relationship Between Laminated Disc and Cone Part

Referring to FIG. 6, a positional relationship between a laminated discD placed on the upper surface of the rubber 125 as the placement surfaceand the cone part 122 is described. FIG. 6 is a schematic sectional viewin the axial direction, which shows a state where the laminated disc Dis placed in FIG. 2.

The laminated disc D includes a lower-side disc substrate D1 on therubber-125 side and an upper-side disc substrate D2 laminated on anupper surface of the lower-side disc substrate D1. Central through holesD1 a and D2 a are formed in the lower-side disc substrate D1 and theupper-side disc substrate D2.

A curved surface part 122 c 3 protruded radially outward is formed in apart where the abutting portion 122 c 2 and the guiding part 122 c 1 arecoupled with each other in the cone part 122. In the presence of thecurved surface part 122 c 3, the lower-side disc substrate D1 of thelaminated disc D can be favorably guided from the guiding part 122 c 1to the abutting portion 122 c 2.

A border part BL between the lower-side disc substrate D1 and theupper-side disc substrate D2 radially overlaps with the curved surfacepart 122 c 3. Therefore, the upper-side disc substrate D2 radiallyoverlaps with the guiding part 122 c 1 and is provided radially invicinity of the guiding part 122 c 1. More specifically, a dimension ofa radius from a point C1 at which a virtual plane including the uppersurface of the rubber 125 as the placement surface and the abuttingportion 122 c 2 intersect with each other to a nodal line CJ1 at which astraight line vertical to a rotational axis J1 and the rotational axisJ1 intersect with each other is arranged to be substantially equal to orsmaller than a radius of the central through hole D1 a of the lower-sidedisc substrate D1. By a thickness of the lower-side disc substrate D1, adimension of a radius from a point C2 at which the boundary part BLwhich is a second virtual plane distant from the nodal line CJ1 axiallyupward and a local surface part 122 c 3 which is the outer peripheralsurface of the cone part 122 intersect each other to a nodal line CJ2 atwhich a straight line vertical to the rotational axis J1 and therotational axis J1 is arranged to be smaller than a radius of thecentral through hole D2 a of the upper-side disc D2 by an amount equalto or larger than a maximum shift amount at a radial position which theupper-side disc substrate D2 a is allowed to have relative to thelower-side disc substrate D1. Therefore, the upper-side disc substrateD2 makes no contact with the abutting portion 122 c 2, and thelower-side disc substrate D1 can be used as the basis of the alignment.Thereby, reduction of an aligning accuracy, which occurs when thelower-side disc substrate D1 and the upper-side disc substrate D2contact with each other, can be controlled.

The lower-side disc substrate D1 alone is used for the alignment, whilethe upper-side disc substrate D2 is prevented from making the contact bythe guiding part 122 c 1. Therefore, the angle φ formed by the abuttingsurface 122 c 2 and the rotational axis J1 can be set without any regardto a possible shift when the upper-side disc substrate D2 is laminated.

8) Disc Driving Device

Referring to FIG. 7, a preferred embodiment of the disc driving deviceaccording to the present invention is described. FIG. 7 is a schematicsectional view in the axial direction illustrating the preferredembodiment of the disc driving device.

Referring to FIG. 7, a disc driving device 200 includes a housingcabinet 201, a brushless motor 203 which is placed in the housingcabinet 201 and rotates a detachable disc 202 in a predetermineddirection, an optical pickup mechanism 204 for recording and reproducinginformation at a required position of the disc 202, an optical pickupmovement mechanism 205 capable of moving the optical pickup mechanism204 in a predetermined direction vertical to the rotational axis J1 ofthe brushless motor 203, a clamp member 206 for pressing the disc 202from the axially upper direction and retaining it, and a tray 207 forinserting and discharging the disc 202.

The optical pickup mechanism 204 is a mechanism for recording andreproducing the information with respect to the disc 202 using a laserlight, and mainly includes a light source, an optical system forintroducing the laser light from the light source to the disc 202, and alight-receiving element for receiving a reflected light from the disc202, and the like.

The optical pickup movement mechanism 205 includes a gear train forcoupling the optical pickup mechanism 204 and the optical pickupmovement mechanism 205, and a motor for driving the gear train.

The clamp member 206 is provided at a substantially same position asthat of the rotational axis J1 and axially movable. In a state where thedisc 202 is placed in the chucking device 203 a of the brushless motor203 and aligned, the clam member 206 moves axially downward, and pressesthe disc 202 from the axially upward direction to thereby retain thedisc 202.

The preferred embodiment of the present invention was so far described,however, the present invention is not limited thereto and can bevariously modified within the scope of its right.

For example, in the preferred embodiments, the sleeve 30 supports theshaft 80, however, the present invention is not limited thereto. A ballbearing may alternatively support the shaft 80.

Further, in the preferred embodiments, POM is used as the material forthe cone part 122, however, the present invention is not limitedthereto. A material having a high slidability, such as PEEK(polyetherkelton etherketone), PPS (polyphenylene sulfide), TPE(thermoplastic elastomer) or nylon-based material, may be used as thematerial.

1. A chucking device capable of attaching a disc having a centralthrough hole rotating around a predetermined rotational axis in adetachable manner, the chucking device comprising: a turn table providedto be concentric to the rotational axis and having a placement surfaceon which the disc is placed; a cone part axially movable including anabutting portion positioned on an upper-surface side of the turn table,the abutting portion having a tilting surface a diameter of whichincreases along axially downward direction and retains an innerperipheral surface of the central through hole of the disc with pressureapproximately uniform in a circumferential direction; a guiding portionwhich is a portion of the cone part, the upper-surface having a shape ofa side face of a truncated cone with a diameter of which increases alongaxially downward direction, a radially outer edge of the upper-surfaceconnected to the abutting portion at the upper-edge thereof from anaxially upper direction; a spring provided between the turn table andthe cone part, the spring applying pressure to the cone part towardaxially upward direction; and an end part provided on an upper-surfaceside of the cone part, inhibiting the movement toward the upperdirection beyond a predetermined position; wherein at least a surface ofthe abutting portion of the cone part is made of a resin material whichshows a smaller frictional coefficient against the inner peripheralsurface of the central through hole of the disc than a frictionalcoefficient of a metal material thereagainst.
 2. The chucking device asclaimed in claim 1, wherein the cone part is made of polyacetal oracetal resin.
 3. The chucking device as claimed in claim 1, wherein anangle φ formed by the tilting surface of the abutting portion in thecone part and the rotational axis satisfies the relationship ofapproximately 12 degrees≦φ≦approximately 15 degrees.
 4. The chuckingdevice as claimed in claim 1, wherein a surface roughness Ry of the conepart satisfies the relationship of approximately 5 μm≦Ry≦approximately20 μm.
 5. The chucking device as claimed in claim 1, wherein an axialsurface roughness Rya of the abutting portion in the cone part satisfiesthe relationship of approximately 5 μm≦Rya≦approximately 20 μm.
 6. Thechucking device as claimed in claim 3, wherein a spring force F of thespring satisfies the relationship of approximately 1.2N≦F≦approximately2.0N.
 7. The chucking device as claimed in claim 1, wherein the disc ismade of polycarbonate, and a coefficient of static friction μ betweenthe central through hole of the disc and the abutting portion of thecone part satisfies the relationship of approximately 0.15 approximately0.30.
 8. A brushless motor for rotating a disc having a central throughhole comprising: a chucking device as claimed in claim 1; a rotationalmember to which the chucking device is secured, the rotational memberintegrally rotating around the rotational axis; a fixed member having abearing part for rotatably supporting the rotational member; a rotormagnet rotating integrally with the rotational member; and a statorfacing the rotor magnet, the stator generating a driving force in adirection of the rotation around the rotational axis.
 9. A disc drivingdevice in which a blushless motor for rotating a disc having a centralthrough hole is equipped, comprising: a blushless motor as claimed inclaim 8; a pickup mechanism for recording and reproduction informationwith respect to the disc; a clamp member for retaining the disc bysandwiching the disc between itself and the placement surface; a discmovement mechanism for moving the disc to the placement surface; and ahousing cabinet for housing the pickup mechanism, the clamp member andthe disc movement mechanism.
 10. A chucking device capable of attachinga disc having a central through hole rotating around a predeterminedrotational axis in a detachable manner, the chucking device comprising:a turn table provided to be concentric to the rotational axis and havinga placement surface on which the disc is placed; a cone part axiallymovable including an abutting portion positioned on an upper-surfaceside of the turn table, the abutting portion having a tilting surface adiameter of which increases along axially downward direction and retainsan inner peripheral surface of the central through hole of the disc withpressure approximately uniform in a circumferential direction; a guidingportion which is a portion of the cone part, the upper-surface having ashape of a side face of a truncated cone with a diameter of whichincreases along axially downward direction, a radially outer edge of theupper-surface connected to the abutting portion at the upper-edgethereof from an axially upper direction; a spring provided between theturn table and the cone part, the spring applying pressure to the conepart toward axially upward direction; and an end part provided on anupper-surface side of the cone part, inhibiting the movement toward theupper direction beyond a predetermined position; wherein a surfaceroughness Ry of the cone part satisfies the relationship ofapproximately 5 μm≦Ry≦approximately 20 μm.
 11. The chucking device asclaimed in claim 10, wherein an axial surface roughness Rya of theabutting portion in the cone part, the Rya being measured along theaxial direction, satisfies the relationship of approximately 5 μm≦Ry≦20μm.
 12. The chucking device as claimed in claim 10, wherein the disc ismade of polycarbonate, and a coefficient of static friction μ betweenthe inner surface of the central through hole of the disc and that ofthe abutting portion of the cone part satisfies the relationship ofapproximately 0.15≦μ≦approximately 0.30.
 13. A brushless motor forrotating a disc having a central through hole comprising: a chuckingdevice as claimed in claim 10; a rotational member to which the chuckingdevice is secured, the rotational member integrally rotating around therotational axis; a fixed member having a bearing part for rotatablysupporting the rotational member; a rotor magnet rotating integrallywith the rotational member; and a stator facing the rotor magnet, thestator generating a driving force in a direction of the rotation aroundthe rotational axis.
 14. A disc driving device in which a blushlessmotor for rotating a disc having a central through hole is equipped,comprising: a blushless motor as claimed in claim 13; a pickup mechanismfor recording and reproducing information with respect to the disc; aclamp member for retaining the disc by sandwiching the disc betweenitself and the placement surface; a disc movement mechanism for movingthe disc to the placement surface; and a housing cabinet for housing thepickup mechanism, the clamp member and the disc movement mechanism. 15.A chucking device capable of attaching a disc having a central throughhole rotating around a predetermined rotational axis in a detachablemanner, the chucking device comprising: a turn table provided to beconcentric to the rotational axis and having a placement surface onwhich the disc is placed; a cone part axially movable including anabutting portion positioned on an upper-surface side of the turn table,the abutting portion having a tilting surface a diameter of whichincreases along axially downward direction and retains an innerperipheral surface of the central through hole of the disc with pressureapproximately uniform in a circumferential direction; a guiding portionwhich is a portion of the cone part, the upper-surface having a shape ofa side face of a truncated cone with a diameter of which increases alongaxially downward direction, a radially outer edge of the upper-surfaceconnected to the abutting portion at the upper-edge thereof from anaxially upper direction; a spring provided between the turn table andthe cone part, the spring applying pressure to the cone part towardaxially upward direction; and an end part provided on an upper-surfaceside of the cone part, inhibiting the movement toward the upperdirection beyond a predetermined position; wherein the disc is made ofpolycarbonate, and a coefficient of static friction μ between thesurface of the central through hole of the disc and that of the abuttingportion of the cone part satisfies the relationship of approximately0.15≦μ≦approximately 0.30.
 16. A brushless motor for rotating a dischaving a central through hole comprising: a chucking device as claimedin claim 15; a rotational member to which the chucking device issecured, the rotational member integrally rotating around the rotationalaxis; a fixed member having a bearing part for rotatably supporting therotational member; a rotor magnet rotating integrally with therotational member; and a stator facing the rotor magnet, the statorgenerating a driving force in a direction of the rotation around therotational axis.
 17. A disc driving device in which a blushless motorfor rotating a disc having a central through hole is equipped,comprising: a blushless motor as claimed in claim 16; a pickup mechanismfor recording and reproduction information with respect to the disc; aclamp member for retaining the disc by sandwiching the disc betweenitself and the placement surface; a disc movement mechanism for movingthe disc to the placement surface; and a housing cabinet for housing thepickup mechanism, the clamp member and the disc movement mechanism.